Design and Fabrication of Novel Single- and Dual-band Bandpass Filters with Modern Zero-Degree Feed Structure for Wireless Communications

In this paper, there are three novel bandpass filters (BPFs), consist of single- and dual-band, presented in a same size, which all the filters, have been designed, optimized and finally fabricated and measured, based on a primary structure and using planar microstrip technology. Each of the generated passbands, is resonated by the use of one of the two existing types of resonator structures. The larger resonators, as main-structures of the filter with a stepped-impedance features, by appling 0°-feed structure and electrical coupling in-between, create the first passband at 0.9 GHz. The smaller resonators as sub-structures, with dual-spiral topology, are in the same size and uniform-impedance, and with symmetrical feeding and internal coupling, are embedded in the main-structures to generate and control the higher passband at 1.8GHz. The existence of a cross-coupling between the sub-structures, suppresses any harmonics in the stop-band and generates additional transmission zeros on both sides of the upper passband. Overal dimensions of the innovative filters with a miniaturizing approach, are reduced from 0.163λg*0.09λg to 0.092λg*0.08λg in terms of the guided wavelength, which is the most compacted structure compared with other filters. According to 0.7 dB and 0.5 dB, the obtained insertion losses of the first and second passbands of the dual-band BPF respectively, the lowest losses have been achieved, compared with other examined dual-band BPFs. Finally three prototypes for global systems for mobile communication, were fabricated and measured. A good agreement between the measured and simulated results indicates realizing the goals and ingenious methods of this design.